Nikolas Jacob Cruz was born September 24, 1998 in Margate, Florida and was adopted at birth by Lynda and Roger Cruz. Both his adoptive parents died, Roger at age 67 in 2004, and Lynda at age 68 in November 2017, leaving Cruz orphaned three months before the shooting. Since his mother's death, he had been living with relatives and friends. At the time of the shooting, he was enrolled in a GED program and employed at a local dollar store.
Cruz was a member of the Junior Reserve Officers' Training Corps (JROTC) and had received multiple awards "including academic achievement for maintaining an A grade in JROTC and Bs in other subjects", according to CNN. He was also a member of his school's varsity air rifle team.
Cruz had behavioral issues since middle school, but a Washington Post writer said the student was "entrenched in the process for getting students help rather than referring them to law enforcement." He was transferred between schools six times in three years in an effort to deal with these problems. In 2014, he was transferred to a school for children with emotional or learning disabilities. There were reports that he made threats against other students.
He returned to Stoneman Douglas High School two years later but was banished in 2017 for disciplinary reasons. As he could not be expelled from the Broward County School system completely, he was transferred to alternate placement. The school administration had circulated an email to teachers, warning that Cruz had made threats against other students. The school banned him from wearing a backpack on campus.
Psychiatrists recommended an involuntary admission of Cruz to a residential treatment facility, starting in 2013. The Florida Department of Children and Families investigated him in September 2016 for Snapchat posts in which he cut both his arms and said he planned to buy a gun. At this time, a school resource officer suggested he undergo an involuntary psychiatric examination under the provisions of the Baker Act. Two guidance counselors agreed, but a mental institution did not. State investigators reported he had depression, autism, and attention deficit hyperactivity disorder (ADHD). In their assessment, they concluded he was "at low risk of harming himself or others". He had previously received mental health treatment, but had not received treatment in the year leading up to the shooting.
Broward County Sheriff Scott Israel described Cruz's online profiles and accounts as "very, very disturbing". They contained pictures and posts of him with a variety of weapons, including long knives, a shotgun, a pistol, and a BB gun. Police said that he held "extremist" views; social media accounts that were thought to be linked to him contained anti-black and anti-Muslim slurs. YouTube comments linked to him include "I wanna die Fighting [sic] killing shit ton [sic] of people", threats against police officers and "antifa," and intent to mimic the University of Texas tower shooting. In February 2017, Cruz legally purchased an AR-15 style semi-automatic rifle from a Coral Springs gun store, after having passed the required background check. Previous to the purchase he had similarly obtained several other firearms, including at least one shot gun and several other rifles. At the time of the shooting, in Florida, it was legal for people as young as 18 to purchase guns from federally licensed dealers, including the assault style rifle allegedly used in the shooting. The minimum age requirement has since been raised to 21.
Items recovered by police at the scene included gun magazines with swastikas carved in them. One student claimed that Cruz had drawn a swastika and the words "I hate niggers" on his backpack. CNN reported that Cruz was in a private Instagram group chat where he expressed racist, homophobic, antisemitic, and anti-immigrant (xenophobic) views. He said he wanted to kill gay people and Mexicans, and talked about keeping black people in chains. He said he hated black people "simply because they were black," and Jewish people because he believed "they wanted to destroy the world." He also referred to white women who engaged in interracial relationships as traitors.
A former classmate said Cruz had anger management issues and often joked about guns and gun violence, which included threats of shooting up establishments. The brother of a 2016 graduate described him as "super stressed out all the time and talked about guns a lot and tried to hide his face". A student who was enrolled at the school at the time of the shooting said, "I think everyone had in their minds if anybody was going to do it, it was going to be him." A classmate who was assigned to work with him in sophomore year said, "He told me how he got kicked out of two private schools. He was held back twice. He had aspirations to join the military. He enjoyed hunting." A student's mother said that he also bragged about killing animals. A neighbor said his mother would call the police over to the house to try to talk some sense into him.